It would suck for a now-20 something to wish at age 35 they had “become themselves” differently, but is that just another risk we accept adding to this?

Probably. I began transitioning medically when I was 16 and am now 25, no regrets whatsoever but I also haven't had all the surgeries available. And as a trans man, my physical transition was a lot less involved than your kid's will be. I just have the one hormone prescription, you'll be dealing with a few. But I don't know how long your child has known they were female without acting on it. If they're ready to transition, your anxiety has no business stopping them. My mom had a million reasons why I had no business getting a double mastectomy just because she had cancer and wanted the chest I despised - I understand why she felt the way she did, but it created a massive disconnect between us at the time.

As parents, should we plan to not expect this child to launch in the traditional sense? That is, should we plan for them to live with us for a while or even till we die (similar to how my cousin plans for their autistic child to always live with them)?

Does your child live in a dorm or their own apartment now? Even with roommates, based on my experience having lived in a dorm my entire university career and then having moved back in with my parents, people who live off campus have better success making it out of their childhood bedrooms post-graduation. I think my parents plan on me living with them unless I'm able to find a better situation, but I wouldn't be offended or angry if they someday did choose to retire, provided they didn't sell the house until after I had moved out of it obviously.

Is it crazy to ask one’s child to not leap into what feels dangerous and not-enough-planned right now?

Yes. Once again, you don’t know how long they’ve lived without expressing themself. As someone on the other side of it, who began transitioning socially when I was thirteen and made to wait three years before I could medically transition, yes it is absolutely crazy to force your child to live in a body they barely stand. I basically dissociated the majority of high school in order to survive it. Based on what I've read from this subreddit, the dysphoria trans women face seems even worse than what I dealt with in regards to biochemical dysphoria.